Lithium batteries are prepared from one or more lithium electrochemical cells. Such cells typically include an anode (negative electrode) of metallic lithium, a cathode (positive electrode) typically a transition metal chalcogenide and an electrolyte interposed between electrically insulated, spaced apart positive and negative electrodes. The electrolyte typically comprises a salt of lithium dissolved in one or more solvents, typically nonaqueous (aprotic) organic solvents. By convention, during discharge of the cell, the negative electrode of the cell is defined as the anode. During use of the cell, lithium ions (Li+) are transferred to the negative electrode on charging. During discharge, lithium ions (Li+) are transferred from the negative electrode (anode) to the positive electrode (cathode). Upon subsequent charge and discharge, the lithium ions (Li+) are transported between the electrodes. Cells having metallic lithium anode and metal chalcogenide cathode are charged in an initial condition. During discharge, lithium ions from the metallic anode pass through the liquid electrolyte to the electrochemically active material of the cathode whereupon electrical energy is released. During charging, the flow of lithium ions is reversed and they are transferred from the positive electrode active material through the ion conducting electrolyte and then back to the lithium negative electrode.
Lithium batteries, with metallic lithium electrodes, have a limited life cycle due to the degradation of the metallic lithium electrodes. Lithium is attacked and/or passivated by electrolytes. This results in formation of lithium powder with a very high surface area at the interface between the metallic lithium and the electrolyte. The formation of high surface area lithium powder is undesirable because it reacts violently with moisture and air.
It has recently been suggested to replace the lithium metal anode with a carbon anode, that is, a carbonaceous material, such as non-graphitic amorphous coke, graphitic carbon, or graphites, which are intercalation compounds. This presents a relatively advantageous and safer approach to rechargeable lithium as it replaces lithium metal with a material capable of reversibly intercalating lithium ions, thereby providing the sole called "rocking chair" battery in which lithium ions "rock" between the intercalation electrodes during the charging/discharging/recharging cycles. Such lithium metal free cells may thus be viewed as comprising two lithium ion intercalating (absorbing) electrode "sponges" separated by a lithium ion conducting electrolyte usually comprising a lithium salt dissolved in nonaqueous solvent or a mixture of such solvents. Numerous such electrolytes, salts, and solvents are known in the art. Such carbon anodes may be prelithiated prior to assembly within the cell having the cathode intercalation material. However, such preintercalation may present problems as it is known that prelithiated carbon electrodes are highly reactive. Such carbon anodes are preferably lithiated in situ. In one embodiment, such prelithiation occurs against a metallic lithium electrode which is later replaced with the cathodic active material electrode of the final cell. In another embodiment, the carbon-based negative electrode is assembled with lithium-containing cathode and/or lithium-containing electrolyte which provides the necessary lithium to form an Li.sub.x C anode in situ. In such a case, in an initial condition, such cells are not charged. In order to be used to deliver electrochemical energy, such cells must be charged in order to transfer lithium to the carbon from the lithium-containing cathode and/or electrolyte. During discharge, the lithium is transferred from the anode back to the cathode as described above.
One drawback of the carbon anode is that upon initial charging of the cell, when lithium is intercalated into the host carbon, some irreversibility occurs in which lithium and/or the cell electrolyte are consumed, resulting in an initial capacity loss for the cell and a reduction of the cell's overall performance. For example, when the anode material Li.sub.x C is prepared in situ in a cell in order to obtain a state of charge and render the anode to a reduced state, some of the lithium which is transferred to the anode upon initial charging, is irretrievably intercalated into the anode in an irreversible process. Some of the intercalated lithium is, therefore, not deintercalated from the anode during subsequent discharge resulting in the loss of capacity since lithium is not available for electrochemical interaction to produce electrical energy. The progressive loss of capacity during use is referred to as "capacity fade".
Based upon the short comings of such carbon-based cells there remains a need for electrochemical cells that are capable of providing improved performance. Therefore, what is needed is an improved anode material which is an alternative to present metallic lithium anodes and a compatible electrolyte which simultaneously fulfills the requirement of high reactivity, good charge rate capabilities, acceptable life cycle, specific rate, stability, and low cost. There is also needed an improved electrochemical cell which does not suffer the initial loss of cycling capability and the further progressive loss known as capacity fade during use.